This application is a 371 of PCT/KR00/00636 filed Jun. 15, 2000.
The present invention relates to a process for preparing biodegradable microspheres containing a biologically active agent comprising: i) preparing a polymer solution containing the biologically active agents by dissolving a biodegradable polymer in a water soluble organic solvent followed by dissolving or suspending the physiologically active agents in the polymer solution; ii) forming an O/O emulsion by emulsifying the biological agents containing polymer solution into a water soluble alcohol which contains, an emulsion stabilizer; iii) extracting the water soluble organic solvent-and water soluble alcohol by adding the O/O emulsion into a neutral or alkaline aqueous solution, and precipitating and educing the microspheres containing the physiologically active agent from the solution. Particularly, the present invention relates to a method of producing sustained-release microspheres, having uniform size, which are compatible with a living body and have an excellent inclusion efficiency.
There is an increasing interest in developing a drug delivery system which is both safe and which provides for a high biological availability of the drug, i.e. to maximize pharmaceutical activity of known drugs as well as to minimize the side effects thereof. Due to their uniform release rate during the given time period and the non-toxic property of the degradation products, biodegradable polymers have been widely investigated as drug carriers. Biodegradable polymer drug carriers are especially useful for delivering drugs requiring continuous and sustained release with a single bolus administration, e.g. peptide or protein drugs, which should be administered daily because of quick loss of activity in the body.
Aliphatic polyesters, such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), copolymers of PLA and PGA (PLGA) or poly(carprolactone) (PCL), and polyanhydrides have been widely used for biodegradable polymers. They can be formulated as various shapes, such as films, strips, fibers, gels or microspheres, and the physiologically active agents are incorporated into the formulations and administered intramuscularly or subcutaneously. However, microspheres have been a particularly preferred formulation because the drug release rate can be easily controlled and the small microsphere particle sizes of 1xcx9c500 xcexcm enables direct injection into the body by conventional methods. Preparation methods, however, to achieve uniform particle size of the microspheres and effective loading of drugs are still under investigation.
Microspheres have been prepared by various methods: solvent evaporation, phase separation, spray-drying, or solvent extraction at low temperature. However, improved methods for preparing microspheres having uniform particle size and effective drug loading are desirable. According to the solvent evaporation method, a hydrophobic polymer is dissolved in a water-immiscible organic solvent, such as dichloromethane, chloroform, or ethyl acetate, to give a polymer solution. Then, a physiologically active agent is dissolved or suspended in the polymer solution. The resulting solution is added into an aqueous solution of a surfactant to form an emulsion system, and microspheres are obtained by evaporating the solvent under vacuum or heating. Although this method is useful for very poorly water-soluble drugs it has very low loading efficiency for water-soluble drugs.
Ogawa et al. discloses a w/o/w double emulsion method for incorporating a water-soluble drug into microspheres (EP 190,833, U.S. Pat. No. 4,954,298, U.S. Pat. No. 4,652,441, and Korean patent 92-7831). According to their method, a biodegradable polymer is dissolved in a water-immiscible organic solvent to give a polymer solution, and a water-soluble physiologically active agent is emulsified into the polymer solution to give a w/o emulsion system. This emulsion is emulsified again into an aqueous solution of a surfactant to produce the w/o/w double emulsion system. The microspheres containing the water-soluble physiologically active agent are obtained by evaporating the solvent. This method requires gelatin be used to increase the viscosity of the w/o emulsion and the loading efficiency decreases remarkably because the particle size of the microsphere is less than 10 xcexcm
U.S. Pat. No. 4,675,189 discloses a phase separation method for preparing microcapsules. In this method an aqueous solution of a physiologically active agent is added into a polymer solution in an organic solvent to give a w/o emulsion. When the temperature, pH, or ionic strength of the w/o emulsion are changed or when a phase separating agent is added into the w/o emulsion, the polymer is precipitated around the water drops of the w/o emulsion.
Spray drying methods can also be employed for preparing microspheres, but this method has limitations due to the high temperatures required during processing. Spray drying methods require high temperatures for evaporating the solvent, and thus, they are not applicable for drugs that are unstable at high temperatures. In addition, a very low yield of microspheres also limits the use of this method.
Gombotz et al., U.S. Pat. No. 5,019,900, discloses a solvent extraction method wherein a physiologically active agent is dissolved or suspended into a polymer solution in an organic solvent, the resulting fluid is sprayed into a liquid of very low temperature, such as liquid argon, nitrogen or oxygen, and the organic solvent is extracted by cold ethanol from the frozen products. This method provides high loading efficiency of the drug, and is applicable for peptide or protein drugs that lose their biological activity easily at high temperatures. There are, however, several disadvantages of this method. For example, a special device is required for spraying the organic solvent; the porosity of the microspheres caused by the rapid freezing in the process results in rapid release of the drug from the microspheres; and some handling problems may arise from the use of liquid of very low temperature, such as liquid argon, nitrogen or oxygen.
In addition to the above methods, various other methods for preparing microspheres have also been used. These methods employ toxic organic solvents, e.g. dichloromethane or chloroform, for dissolving a biodegradable polymer such as polylactic acid. It is required that the residual organic solvents in the microspheres be restricted to within very low limits. The use of toxic organic solvents can also cause environmental problems.
Hyon et al., U.S. Pat. No. 5,100,669, discloses a method of preparing microspheres using acetic acid as the organic solvent. A biodegradable polymer and a physiologically active agent are dissolved in an aqueous solution of acetic acid, and the resulting solution is emulsified into water-immiscible oil (e.g. paraffin, mineral oil, and vegetable oil) or an organic solvent (e.g. toluene, xylene, and hexane) to give an O/O or w/o emulsion. The microspheres are obtained by evaporating the acetic acid. This method provides microspheres having a high drug-loading efficiency and with various particle sizes ranging from 0.01 to 300 xcexcm. However, acetic acid should be evaporated at high temperature for longer than 12 hours due to its high boiling temperature (118xc2x0 C.), and especially, the organic solvents (e.g. pentane, hexane, or heptane) which are used for separating the microspheres from the oil phase are toxic to the body and may cause environmental problems.
Therefore, a method of preparing efficiently, within a short time, a microsphere having good biocompatibility, high loading efficiency of a physiologically active agent, and uniform particle size, without use of a non-toxic organic solvent is greatly needed.
It is an object of this invention to provide a process which does not require use of a toxic organic solvent and the resulting microspheres have good biocompatibility, high loading efficiency of a physiologically active agent, and uniform particle size.
Further features of the present invention will appear hereinafter.